Title

Author

Date

March 2010

Document Type

Thesis

Degree Name

M.S.

Institution

Oregon Health & Science University

Abstract

Actin crosslinkers are essential for the highly specified structure of hair cell stereocilia. Crosslinkers are known to influence the length, diameter and stiffness of actin-based cell protrusions, all qualities that are integral to stereocilia function. Using mass spectrometry, our lab has identified several abundant actin crosslinkers, including fascin-1, fascin-2, plastin-1, plastin-2 and plastin-3. The expression patterns and functions of these crosslinkers during hair cell development have been studied very little. Because of preliminary evidence that one of these crosslinkers, fascin-2, is developmentally regulated, I analyzed fascin-2 during stereocilia development in chicken basilar papilla. Fascin-2 mRNA and protein levels increase at each time point examined, with the largest increases during periods of stereocilia elongation. In mature bundles, fascin-2 is concentrated in the distal portion of the tallest stereocilia. At early stages of stereocilia development, fascin-2 is present in cell bodies and in stereocilia. As bundles mature, fascin-2 is exclusively localized to the distal regions of stereocilia. mRNA levels of the complement of fascin and plastin genes showed a complex developmental expression pattern: fascin-1 decreased, fascin-2 increased, plastin-1 increased, plastin-2 increased then decreased, and plastin-3 stayed constant. These findings suggest that different crosslinkers may be involved in distinct phases of stereocilia elongation and widening, as well as in the long-term structural integrity of the bundle.

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